function hiirca_hui, T

  T_HI = 1.57807d5
  lambda = 2.d0 * T_HI / T

  rate = 1.269d-13 * lambda^1.503d0 / $
         ( 1.d0 + (lambda/0.522d0)^0.470d0 )^1.923d0

  return, rate

end
